Cuvette

ABSTRACT

A cuvette for taking up a fluid and mixing the fluid with a reagent for analyzing the mixture consists of a body (10) of glass or polymeric material having a first cavity (12) in which the fluid can be taken up, preferably by capillary action, through an inlet (13), and at least one further cavity (21) exerting capillary force on fluid which is transported from the first cavity (12) into a reception cavity (17) by subjecting the cuvette to centrifugal force. The further cavity (21) preferably exerts capillary force through a wick (19) which does not extend as far as the bottom of the reception cavity (17), and a capillary channel (20). In those cases where more than one further cavity (21) is provided, each such cavity (21) communicates with a further reception cavity into which the fluid can be transported from the cavity (21) by the exertion of centrifugal force. The cuvette may also have cavities for receiving washing or diluting liquid, which are connected in series or in parallel with the cavity (12).

The present invention relates to a cuvette for taking up at least onefluid and mixing the fluid with a reagent for analysing the mixture, thecuvette having at least one first cavity in which the fluid can be takenup through an inlet.

A cuvette of this type, which is used for direct optical analysis of themixture, is previously known from U.S. Pat. No. 4,088,448. The cuvetteaccording to this patent consists of a body member having two flatsurfaces forming an optical path and spaced a predetermined distancefrom each other for determining the length of the optical path, anddefining a cavity having an inlet by means of which the cavitycommunicates with the ambient atmosphere. The cavity has a predeterminedfixed volume, and the predetermined distance between said surfacesenables the cavity to take up a sample by capillary action. Further, areagent is applied to the surfaces of the cavity.

This known cuvette offers many advantages over other prior artapparatuses of the same type. By means of the cuvette, a fluid can betaken up, mixed and chemically reacted with a suitable reagent, e.g. forcolour development in the same cavity as is used for the subsequentmeasuring operation. Thus, the cuvette according to U.S. Pat. No.4,088,448 simplifies the sampling procedure, reduces the amount ofaccessory equipment and in most cases--depending on the type ofanalysis--considerably increases the accuracy of the analysis by makingthe analysis procedure independent of the skill of those carrying outthe analysis.

The cuvette according to U.S. Pat. No. 4,654,197 increases the number ofreactions possible in a cuvette system, by using a semipermeablemembrane as a functional part of the cuvette.

The object of the present invention is to further improve these knowncuvettes and to that end, the new cuvette is characterized in that ithas, in addition to said first cavity, at least one second cavityadapted to take up fluid from the first cavity by capillary actionwithout any external influence via a first channel having means foradmitting fluid therein by external influence only, preferably by theexertion of centrifugal force, and that at least the second cavitycontains a reagent or a fluid-modifying agent.

Thus, the cuvette according to the invention has at least two cavitiesdefined by surrounding walls, viz. a first cavity or inlet cavity inwhich the fluid is taken up, preferably by capillary action through theinlet, and a second cavity in which the fluid can be taken up aftercentrifugation of the cuvette. Preferably, a reception cavity isprovided which communicates with the first cavity through said channel.The reception cavity can be said to be divided into two sections, viz. afirst, lower section for receiving heavy material taken up in the fluid,and a second, upper section forming the second cavity and serving asmeasuring cavity. Instead of relying on centrifugal force for fluidtransport through the channel, it is also possible to exert a pressureon the fluid in the first cavity, which however presupposes a ventingdevice. The walls of the cavities, the reception cavity and the channel,or a desired portion thereof, may be coated with reagent or the like,and an analysis can be carried out on fluid in both the first cavity andthe second or the capillary section of the reception cavity, and also inthe heavier-material section of the reception cavity.

From e.g. U.S. Pat. No. 4,462,964 and U.S. Pat. No. 4,714,590 it ispreviously known, in an analysis cuvette, to provide capillary orificesin the fluid path. As opposed to the arrangement according to theinvention, these orifices however serve to prevent fluid transport untilthe cuvette is subjected to centrifugation. During centrifugation, thefluid is pressed through the capillary orifices into the analysis cells.The special means which in the cuvette according to the inventionprevents fluid from entering the channel might be in the form ofcapillary orifices as in the known devices, but such orifices wouldprobably not be more effective than the hydrophobic filter materialused. The capillary device provided between the channel of the cuvetteaccording to the invention and its second cavity performs its functionwithout any external influence.

One advantage of the improved cuvette according to the invention is thatit can be used for whole blood sampling even if the analysis must beperformed on plasma or serum. Thus, the cuvette can be used for analyseswithin a much broader range than the cuvettes according to U.S. Pat. No.4,088,448 and U.S. Pat. No. 4,654,197. Another major advantage overprior art cuvettes is that the use of the centrifugal force makes itpossible to carry out different reactions in different cavities, thusallowing a period of incubation before the next reagent is used. Yetanother advantage is that such material as is produced or used in areaction, such as precipitated proteins or immunoaggregates, which mightotherwise interfere with subsequent reactions or measurements, can beseparated by centrifugation.

The cuvette can be manufactured from glass or polymeric material. It isalso possible to manufacture it from many other materials, e.g.different types of semi-permeable materials, like the cuvette accordingto U.S. Pat. No. 4,654,197, or optically transparent or non-transparentmaterials. The reagent, which is provided in at least one cavity, can bedeposited by evaporation, freeze-drying, spraying, screen-printing or byother techniques.

The functional parts of the cuvette may vary depending on the fluid tobe analysed and the type of analysis. If the inlet cavity should take upthe fluid by capillary action, the distance between the cuvette wallsmust be less than 1 mm, and preferably 0.7 mm. If this is not the case,the capillary action must be brought about by other means than thewalls, and the wall material must be wettable with the fluid or treatedto be so. The volume of the inlet cavity depends on the need of fluid inthe succeeding cavities and the amount of material to be separated bycentrifugation. The channel connecting the first cavity to the second orthe reception cavity has low capillary action, i.e. the distance betweenthe walls exceeds 0.7 mm. The walls defining the channel may suitably bemanufactured from non-wettable material or treated so as to benon-wettable. The channel may also contain non-wettable filteringmaterial or other means for preventing spontaneous transport of fluidfrom the first cavity. Thanks to this arrangement, the amount of fluidtaken up becomes fairly exact and can be determined by the manufacturingprocess. By a suitable design of the channel, it can also be used formixing the fluid passing through it during the centrifugation and, asindicated above, may also be provided with a reagent.

Of the two reception cavity sections, the lower section has, as statedabove, low capillary action between the walls, whereas the upper sectionhas high capillary action. The upper section merges into the lower via aportion which can be referred to as a "wick". The "wick" may consist ofcapillary channels in the cuvette walls, but may also consist of atraditionally operating wick of a special design. Fluid is thus drawnfrom the lower section into the upper by capillary action as soon as thecentrifugal force ceases acting.

The invention will be described in more detail hereinbelow withreference to the accompanying drawings schematically illustrating someembodiments.

FIG. 1 is front view of a basic embodiment of the invention,

FIG. 2 is a longitudinal section of this embodiment, and

FIGS. 3-8 are front views of other embodiments of the invention havingdifferent numbers of cavities and reception cavities of modifieddesigns.

The cuvette in FIGS. 1 and 2 has a first wall 10 of glass or polymericmaterial and a second wall 11, also of glass or polymeric material. Thewalls 10 and 11 may also comprise several other materials, such asoptical windows, semipermeable membranes, electrode material or othertechnical means. The walls 10, 11 define a plurality of cavities ofdifferent depths. A first cavity 12, or inlet cavity is adapted to takeup a liquid sample and has such a depth that it can be filled bycapillary action through a capillary inlet 13 communicating with theambient atmosphere. However, it is also conceivable to fill this cavityby injecting the liquid sample, although one of the advantages of theinvention will then be lost. The first cavity 12 may be provided with areagent, that is an agent for reacting with the liquid sample drawn intothe cavity. The reagent may be deposited on the walls of the cavity byevaporation, freeze-drying, spraying, screen-printing or in any othersuitable way, depending on how the cuvette is manufactured. The firstcavity 12 may also contain an agent otherwise modifying the sample. Thefirst cavity 12 passes into a channel 14 which owing to its depth, asshown in FIG. 2, exerts low capillary action on the liquid received inthe inlet cavity and has walls of hydrophobic material or walls treatedwith such a material. Further, the channel may also be provided with ahydrophobic filtering material, as shown at 15. These measures can alsobe combined. Further, the channel 14 may include a reagent or amodifying agent. The channel 14 opens into a reception cavity 16, 17divided into two sections, viz. an upper section 16, which may also bereferred to as "second cavity", and a lower section 17. The uppersection or second cavity 16 exerts capillary action because of the smalldistance between the walls, as shown in FIG. 2, whereas the lowersection 17, like the channel 14, does not exert any capillary actionbecause of its greater depth. The walls of the lower section may betreated in the same way as the walls of the channel. Between the uppersection or second cavity 16 and the lower section 17, there is provideda wick 18 connected to the upper section, but terminating at a certaindistance from the bottom of the lower section. This "wick" 18 may be aconventional wick of any suitable material, but may also consist ofspecial capillary slots in the cuvette walls or formations thereon.

When using the cuvette according to FIGS. 1 and 2, the first cavity 12is filled with a liquid sample which in the illustrated embodiment isdrawn into the cavity by capillary action through the inlet 13. Theliquid sample mixes with reagent or the like provided in the cavity 12,and the mixture can then be analysed, e.g. in a photometer. If thecuvette is thereafter subjected to centrifugal force, the liquid sampleor a portion thereof present in the cavity 12 can be caused to passthrough the channel 14 and, during centrifugation, reach the lowersection 17 of the reception cavity. When centrifugation thereafterceases, a portion of the liquid sample will be drawn up into the uppercapillary section 16 by means of the wick 18. Since the wick 18 does notreach as far as the bottom of the lower section 17, heavier materialwill remain therein, thus allowing separation of material. The volumesof the different cavities or sections must be so related to each otherand to the volume of heavier material taken up or produced in the liquidsample, that no part of the cuvette will be excessively filled orreceive an insufficient amount of fluid. Depending on the analysis to bemade, neither, one or both of the sections 16, 17 can be provided with areagent or a modifying agent. An analysis can then be made on the liquidin the upper section 16 and also on the heavier material in the lowersection 17. Examples of heavier material are blood cells collected inthe section 17 when analysing a blood sample.

FIG. 3 shows an embodiment of the invention which is more useful inpractical application. The cuvette may be designed in the same way as inFIGS. 1 and 2 and has a first cavity 12 with an inlet 13, a channel 14with hydrophobic obstacles and a reception cavity 17. However, the uppersection or second cavity, here designated 21, of the reception cavity isoffset with respect to a centre line passing through the first cavityand the lower section of the reception cavity 17. The second cavity 21communicates with the reception cavity 17 by a capillary channel 20making an angle with the centre line passing through the first cavity 12and the reception cavity 17. A capillary formation or wick 19 of thesame type as the wick 18 is connected with one end to the Capillarychannel 20 and extends a certain distance downwards towards the bottomof the section 17, but terminates at a safe distance therefrom for thesame reason as in the previous embodiment. The second cavity 21 is hereconnected to a venting device in the form of a channel 22 opening intothe ambient atmosphere for preventing the formation of air inclusions.In this cuvette, the measuring or reaction cavity 21 is thus not locatedin the fluid path existing during the centrifugation of the cuvette andmay thus be provided with a reagent incompatible with the heaviermaterial in the liquid. This simple cuvette solves a number of analysingproblems. Reagents or other agents can be deposited in several places bydifferent techniques. Incubations over suitable times are possible inthe first cavity 12 and in the reception cavity 17 during centrifugationand, of course, in the second cavity 21. If several reagents or the likeare required on different occasions after a separation process, thecuvette must have more than three cavities, where a second cavity servesas an inlet cavity for a new cycle of centrifugation, as will appearfrom the following description.

The cuvette in FIG. 4 thus has a second reception cavity 28communicating with the second cavity 21 through a channel 27 which, likethe channel 14, is provided for Preventing spontaneous liquid transportby capillary action. The second reception cavity 28 r-an be used as afurther measuring cavity and may be provided with a reagent or the like.Liquid present in the second cavity 21 can be caused by centrifugationto pass through the channel 27 to be taken up in the reception cavity28. After a predetermined time and optionally after mixing with areagent, the liquid can be subjected to analysis in the cavity 28. Oneof the advantages of this embodiment of the invention is that a reagentcan be provided in the cavity 21 and the liquid received there passed,after a predetermined time of incubation, to the reception cavity 28after centrifugation of short duration, and the liquid is then mixed inthe cavity 28 with a new reagent or the like in order to be analysedafter a predetermined time of incubation.

FIG. 5 shows an embodiment which, in addition to the first cavity 12,the channel 14 and the reception cavity 17, has a second cavity 21, athird cavity 21' and a fourth cavity 21" as well as a second channel 14'and a third channel 14", a second reception cavity 17' and a thirdreception cavity 17" as well as a first capillary channel 20, a secondcapillary channel 20' and a third capillary channel 20". A liquid takenup in the first cavity 12 is passed, as described above, into thereception cavity 17 by centrifugation, from where it is taken up in thesecond cavity 21 by capillary action through the wick 19 and thecapillary channel 20. From the second cavity 21, the liquid istransported to the reception cavity 17' via the channel 14', also bycentrifugation, to be drawn from there up into the third cavity 21' bymeans of a wick 19' in the same manner as in the preceding step.Similarly, the liquid is taken up in the fourth cavity 21" via thereception cavity 17", the wick 19" and the channel 20". There are notvery many analyses having such a complicated reaction pattern as tonecessitate a cuvette of the embodiment now described. However, thisembodiment clearly shows the versatility of the invention. In thelast-mentioned embodiment, the venting channel 22 is connected to thelast cavity 21" in the series of cavities.

FIG. 6 shows a further embodiment which is a combination of theembodiments of FIGS. 3 and 4. Thus, to a reception cavity 17 areconnected two channels 20, 24 which are each connected to a secondcavity 21, 25 and each have a wick 19, 23. The cavities 21, 25 each havea venting channel 22 and 26, respectively. The embodiment in FIG. 6 canbe used for performing two analyses which must be carried out afterdifferent times of incubation. Since two analyses can be performed aftera single centrifugation, the cuvette according to FIG. 6 can betime-saving in many cases.

One practical example of the versatility of the invention is theanalysis of urea and alkaline phosphatase from whole blood in thecuvette according to FIG. 6. The cuvette wall 10 with the recessesdefining the cavities can be manufactured from cellulose-based resinwhile the other wall, forming a lid, can be cut from a sheet of the samematerial.

The surfaces of the cavities depending on capillary force can be treatedby corona discharge or in any other way for increasing wettability. Thehydrophobic channels 14, 14', 14" and 27 can be treated with siliconefluid, and a filter consisting of a small piece of sinteredpolypropylene can be pressed into place in the upper part of thesechannels. A mixture of glycine, magnesium chloride, paranitrophenylphosphate and a carrier agent, giving a pH of 10.5 when dissolved inplasma, is printed on one or both of the large surfaces defining thesecond cavity 21. On the surfaces defining the cavity 28 in FIG. 6 isprinted a mixture of sodium hydroxide and a carrier agent. To one of thewalls defining the cavity 25 is applied a mixture of urease and analkaline buffer, and on the corresponding area of the opposite wall isapplied a substantially transparent material of cellulose estercontaining a pH indicator with an indicator range within the acid area.The first cavity 12 and the reception cavity 17 may contain heparin toprevent coagulation If the reaction time is long. The two walls whichaccording to FIG. 2 form the cuvette can be joined together by weldingor gluing. Both methods give excellent results.

In the use of a cuvette according to FIG. 6, which has been treated inthe manner just described, the cuvette is contacted with a whole bloodsample and placed in a special centrifuge photometer. Centrifugation isstarted, and the blood is passed into the reception cavity 17. After60-90 seconds, the blood cells have been separated, and the centrifugeis stopped. Plasma is now drawn up into the cavities 21 and 25 throughthe channels 20 and 24. The photometer may have an initial measurementas reference, otherwise analysing starts by monitoring the kineticturnover or reversal of the pH indicator because of the ammonia producedby the urease action on the sample urea in the cavity 25. As the ureavalue is read, the alkaline phosphatase reaction proceeds in the secondcavity 21 and after a predetermined time, the centrifuge is started inorder, after a short time, to bring the reaction to a stop when theliquid has been contacted with the sodium hydroxide in the cavity 28,which also develops a yellow colour of digested substrate. Aftermeasuring the colour in the cavity 28, the data received is processedand the analytical values are presented.

It may sometimes be desirable to dilute or wash the drawn-up fluid witha liquid which should be applicable in one or more cavities providedtherefor. To this end, a cuvette of the design shown in FIG. 7 can beused. Here, the cavity 12 is connected in parallel with a cavity 30 fortaking up said liquid. The two cavities 12 and 30 each have an outletchannel 33 and 34, respectively, both of which open in the channel 14.During centrifugation, fluid and liquid in the cavities 12 and 30,respectively, will flow into the channel 14 and through this channelinto the reception cavity 17 and so forth, as in the precedingembodiments.

The diluting or washing liquid can be sucked into the cavity 30 inconnection with the analysis, but it can also be supplied in advance,suitably when applying the reagent, in which case the liquid must besealingly enclosed, which can be done by means of sealing plugs ormembranes provided in the inlet and the outlet of the cavity. It is alsoconceivable to place a capsule of suitable material in the cavity 30.When the cuvette is to be used, the two seals can be penetrated by meansof a suitable tool. It is also possible, as illustrated at 36, toprovide some type of perforation means 36 in the cavity. When thecuvette is subjected to centrifugation, the perforation means 36 willthus be urged into engagement with the seal 35 in the outlet so as topenetrate it.

It is also conceivable to connect the cavity with washing or dilutingliquid in series with the fluid reception cavity 12. This can be done,for instance, by modifying the cuvette according to FIG. 5 in the wayshown in FIG. 8. The cavity, which in the embodiment according to FIG.5, serves as second cavity 21 is here used as first cavity 12 by beingprovided with an inlet 39. The first cavity in FIG. 5 here forms acavity 38 for receiving diluting or washing liquid which, like the fluidin the embodiments described above, is supplied by means of a channel41, a reception cavity 40 and a liquid-drawing capillary formation 42,to the fluid reception cavity 12 and transported, if so desired, to thesucceeding cavities in the same manner as in the embodiment of FIG. 5.The diluting or washing liquid can be drawn into the cavity 38 bycapillary action in connection with the analysis, but many times it isinstead more conveniently applied in advance and sealingly enclosed inthe cavity in the same manner as in the cavity 30 in FIG. 7.

In certain analyses, it may be desirable to retain part of the fluid orthe diluting or washing liquid which by the centrifugation has reachedthe respective reception cavity 17 and 40, in this cavity. Suitably, thecavity is widened, as shown at 37, so as to have a volume exceeding thevolume of the cavity 21 and 12, respectively. After a secondcentrifugation, in which e.g. the cavity 21 has been emptied, fluid istherefore again drawn up from the cavity 17.

The drawings show all the cavities as defined by sealing walls, but itis evident that one or some of these walls can be replaced by asemipermeable membrane, as stated in U.S. Pat. No. 4,654,197.

The invention will be further illustrated by Examples 1 and 2, relatingto the determination of hemoglobin and glucose in whole blood, andglucose and protein in serum or plasma, respectively, using the cuvettedescribed above.

EXAMPLE 1 Determination of Hemoglobin and Glucose in Whole Blood

The red cells of the blood, the erythrocytes, carry inside theirsemipermeable membrane, primarily of lipides and proteins, a pluralityof water-soluble chemical substances of both low- and high-moleculartype. An example of the high-molecular type is the oxygen-transportingprotein hemoglobin and an example of the low-molecular type Is glucosewhich is a necessary energy substance for sustaining metabolism.Low-molecular substances often exist both intra- and extracellularly,while high-molecular substances often cannot pass through the membraneof the erythrocytes. When determining hemoglobin or glucose in wholeblood, the membrane of the erythrocytes is ruptured, e.g. by a detergentor an osmotic shock or a combination thereof, and the substancescontained in the erythrocytes become available for chemical analysis.

Hemoglobin

In a cuvette according to the invention, e.g. FIG. 3, the cavity 12 issupplied with a dry chemical reagent consisting of

0.30 mg sodium deoxycholate

0.15 mg sodium azide

0.15 mg sodium nitrite

0.1 mg non-reactive ingredients

The reagent composition for a certain cuvette quantity is dissolved in asmall amount of water and Pluronic P85®. The reagent composition hassuch a viscous consistency that it can be uniformly applied over thesurface in the cavity 12, e.g. by screen-printing or dabber printing.The reagent Composition used produces, together with hemoglobin, ahemoglobin azide complex which can be determined photometrically in thecavity 21. The cuvette with hemoglobin reagent is used such that thecavity 12 is supplied with whole blood. The reagent dissolves into theblood, and the chemical reaction forming a hemoglobin azide complex isfinished after about 45 seconds. The contents in the cavity 12 aretransferred, e.g. by centrifugal force, into the cavity 21 where a clearlow-turbid solution can be analysed by photometry. The distance betweenthe walls in the cavity 21 is about 0.13 mm.

Glucose

1 kU GDH, glucose dehydrogenase

220 U NAD

0.3 mmol MTT

250 g White Saponin®

50 mg Pluronic P85®

250 μl water subjected to ion-exchange

The components included are finely divided into a suspension which issuitable to be used for coating surfaces by different printingtechniques, such as silk screen printing, cylinder printing etc. Thistype of suspension is suitable for coating cuvettes according to theinvention. In certain cases, surface-tension reducing substances may beadded for facilitating the coating of hydrophobic plastic materials. Inorder to adapt the suspension to different coating equipment, theviscosity can be varied by adding suitable high-molecular polymers. Thechoice of high-molecular polymers is not critical, but affects thedissolving rate of the dry reagent. Among usable polymers may bementioned polyethylene glycol, polyvinyl pyrrolidone, dextran anddifferent cellulose derivatives. The choice of polymer can also be madewith a view to stabilising the suspension. On the basis of knownpreparation techniques in e.g. the foodstuffs or cosmetics industry, thereagent can be adapted to different surfaces.

The reagent for glucose in whole blood is placed, as described above, ina cuvette according to the invention of the type shown in FIG. 3. Theglucose reagent is placed in the cavity 12. The transfer of reagent intothe cavity 21 can be achieved, e.g. by centrifugal action. The cavity 12is filled with whole blood, and the glucose reagent brings about aconversion of glucose into a photometrically measurable colour atend-point after about 3 minutes. The transfer into the cavity 21 can beeffected after the red blood cells, the erythrocytes, have beenruptured, i.e. about 1 minute after. In the same way as in the case ofhemoglobin, photometering is carried out in a low-turbid clear aqueoussolution. The distance between the walls in the cavity 21 is about 0.14mm for glucose determination in whole blood. The photometric method fordetermining glucose and hemoglobin in whole blood is advantageouslyperformed by a two-wavelength measurement.

EXAMPLE 2 Determination of Glucose and Protein in Serum or Plasma

When determining an analyte in plasma or serum, the red blood cells, theerythrocytes, should be excluded. A cuvette according to the inventionis especially well suited for analysing in plasma or serum when thecuvette has several cavities and the communication between the differentcavities is maintained by capillary force and centrifugal force. Bloodis drawn into a cavity, often by capillary force by direct sampling, andplasma or serum is transferred, after centrifugation of the cuvette, bycapillary force into a cavity containing a reagent composition,specifically suited for determining the analyte.

Glucose in Plasma or Serum

Reagent composition, 1 ml:

1 kU GDH, glucose dehydrogenase enzyme

220 U NAD

0.3 mmol MTT

50 mg Pluronic P85®

250 μl water subjected to ion-exchange

The reagent chemicals included are treated as in the previous Examplefor determining glucose in whole blood. Any modification of the reagentcomposition to achieve an adequate function, such as dry reagent, andadhesion to the walls of the cuvette cavity complies with thedescription in the previous Example.

For determining glucose in plasma or serum in a cuvette according to theinvention, the cuvette according to FIG. 3 is advantageously used. Thereagent composition described above is applied in the cavity 21, e.g. byprinting technique, uniformly over the surface thereof. After drying,the reagent passes into what is often referred to as dry reagent. A lidis placed over cavities and other channels in the structure. Whole bloodis sampled and flows into the cavity 12, e.g. by capillary action. Aftersampling, the cuvette is centrifuged, and after completed centrifugationthe cavity 21 is filled with plasma or serum by capillary action. Thered blood cells have been removed by centrifugation and cannot fill thecavity 22. A-he reagent composition dissolves in serum or plasma, andthe chemical reaction permits a specific determination of glucose. Thechemical reaction, i.e. the glucose content, can be read directly in thecuvette by photometric technique.

Protein in Serum or Plasma

Reagent composition:

1 mmol lithium tartrate

1 mmol copper tartrate

7 mmol lithium hydroxide

These chemical substances are dissolved in a suitable amount of water.In order that the solution should be given the correct viscosity forapplication in a cavity by printing technique, the solution isevaporated. The application of the reagent by printing technique isfacilitated if the dry reagent additionally contains about 0.5-2%lithium lauryl sulphate and about 1-5% polyvinyl pyrrolidone/polyvinylacetate copolymer and optionally a plasticiser.

The reagent is applied in the cavity 21 in a cuvette according to FIG.3. The cuvette functions in the same manner as the cuvette used forglucose determination in plasma or serum.

The cuvette according to the invention can be used for many types ofanalyses and is especially well suited for routine-type blood analyses,such as determination of glucose, urea-nitrogen in blood, albumin,bilirubin, total protein etc., particularly on the basis of whole blood,and for a large number of other analyses. Thus, the invention must notbe considered restricted to what has been described above, but may bemodified in several different ways within the scope of the accompanyingclaims.

We claim:
 1. A cuvette for taking up at least one fluid and for mixing afluid with a dry reagent for analyzing a mixture, wherein said cuvettecomprises:a) at least one capillary first cavity having an inlet andconstructed and arranged to take up a fluid by capillary action alone;b) a first channel having a non-capillary and non-spontaneous fluidtransporting function operative only under external influence byapplication of a centrifugal force on the cuvette; c) a centrifugationreception cavity communicating with said at least one capillary firstcavity via said first channel and constructed and arranged to exert nocapillary action: d) at least one capillary second cavity constructedand arranged to take up fluid by capillary force alone; and e) a firstcapillary transporting means projecting into said centrifugationreception cavity, being connected to said at least one capillary secondcavity and constructed and arranged to transport fluid by capillaryaction from said centrifugal reception cavity into said at least onecapillary second cavity.
 2. A cuvette as claimed in claim 1, furthercomprising a capillary channel provided between said reception cavityand said at least one capillary second cavity, an end portion of saidfirst capillary transporting means facing away from said receptioncavity being fixed in said capillary channel.
 3. A cuvette as claimed inclaim 1, further comprising a second reception cavity communicating withsaid at least one capillary second cavity via a second channelcorresponding to said first channel.
 4. A cuvette as claimed in claim 3,wherein said second reception cavity has a second capillary transportingmeans corresponding to said first capillary transporting means andconnected to a second capillary channel opening in a capillary thirdcavity.
 5. A cuvette as claimed in claim 4, further comprising at leasta third reception cavity, a third channel, a third capillarytransporting means, a third capillary channel and a capillary fourthcavity connected to said at least one capillary second cavity via saidcapillary third cavity.
 6. A cuvette as claimed in claim 5, having aplurality of channels and reception cavities, and capillary transportingmans, capillary channels and cavities, wherein all channels andreception cavities extend along parallel lines making an angle withparallel lines along which the capillary channels extend.
 7. A cuvetteas claimed in claim 1, wherein at least two capillary cavities areconnected to each reception cavity.
 8. A cuvette as claimed in claim 1,wherein said capillary transporting means consists of a wick.
 9. Acuvette as claimed in claim 1, wherein all cavities and/or receptioncavities are coated with reagents or fluid-modifying agents.
 10. Acuvette as claimed in claim 1, wherein at least one cavity for receivingdiluting or washing liquid is connected in parallel with said at leastone capillary first cavity, said two cavities having outlets connectedto said first channel.
 11. A cuvette as claimed in claim 1, wherein atleast one cavity for receiving diluting or washing liquid is connectedin series with said at least one capillary first cavity via a channel, areception cavity and a capillary transporting means.
 12. A cuvette asclaimed in claim 10, wherein said cavity for receiving diluting andwashing liquid is provided, at an inlet and an outlet thereof, withmeans for sealingly enclosing a liquid, the means for sealinglyenclosing the liquid provided in said outlet being rupturable by apenetrating means disposed in the cavity and activatable by centrifugalforce.
 13. A cuvette as claimed in claim 1, wherein at least onereception cavity has a larger volume than the succeeding cavities whichare arranged to take up fluid from said reception cavity.
 14. A cuvetteas claimed in claim 1, wherein at least one of the cavities is coveredwith a hydrophillic or hydrophobic semipermeable membrane containing areagent.
 15. A cuvette as claimed in claim 1 in which said capillarysecond cavity is offwet with respect to said first channel and whereinsaid capillary second cavity communicates with the ambient atmospherethrough a vent.
 16. A cuvette as claimed in claim 1 in which saidcapillary second cavity is in line with said first channel and betweensaid first capillary cavity and said centrifugation reception cavity.17. A cuvette as claimed in claim 1 wherein said capillary second cavitycontains a dry reagent or a fluid-modifying agent.